The invention relates to a stacker for flat material such as banknotes, bankpapers and the like, with a cylindrical suction drum, whose casing along at least one generatrix has a line of suction openings, and with a stator, on which the suction drum is turningly bearinged, whose outer face has suction air-ways stretching in the peripheral direction over a certain angle range, and by way of which the suction openings are joined with vacuum dependent on their position in relation to the stator, and the suction drum is designed for suction-gripping, in its suction part, of the material in the tangential point at the leading edge, taking it from the transport system on being further turned, moving it to a clearing unit and letting it off with the forming stack at the point at which the clearing unit takes effect.
In this connection a suggestion has been made earlier in the German Offenlegungsschrift specification No. 2,555,306 for the use of a stacker generally made up of a hollow cylindrical stacker drum turning about the axis of a stator, and a transport system for moving the banknotes to the drum. The stacker drum has a line of suction openings parallel to its long-axis on the outer face of the drum casing. The banknotes are moved to the drum by way of the transport system which is tangential with respect to the stacker drum. The line of suction openings of the stacker drum is so timed in its motion in relation to the line of banknotes being moved up to it that after each turn it comes up against the leading edges of the banknotes, being moved towards it in the timed order, at a tangential point. For stacking, the banknote, suction-gripped at the tangential point, is moved round on the stacker drum till its leading edge comes to the position of stopping, formed by a clearing unit, and is placed on any stack which has been formed here so far.
The suction connection for the line of suction openings is by way of sectorial airways machined in the stator. In this respect, the suction airway in the stator is so placed as to be stretching generally along an angle range from the tangential point to the clearing or stopping point, so that it is only in this range that the suction openings are able to be joined with the vacuum system at an unchanging vacuum level.
This stacker may be worked in the desired way as long as the banknotes are timed in their motion towards the stacker drum, that is to say as long as, in each case, the leading edge of each banknote comes up against the line of suction openings at the tangential point. In general operation it has, however, turned out--because a certain degree of slip in the transport system may not eliminate--the banknotes are not in all cases transported in the necessary timed relation, so that they are suction-gripped by the stacker drum overly early or are not gripped at all. In this respect the banknotes, which are suction-gripped overly early, after running up against the clearing unit, are still suction-gripped by the suction openings and forced against the clearing unit with the outcome that the leading edges are, in most cases, folded or even crumpled. Banknotes which are overly late in their timing and which are not gripped by the stacker, are moved on further uncontrolledly in the transport system and, more specially in connection with the banknotes coming after them, are responsible for the forcing together and jamming of banknotes and stopping of the system.
For overcoming the effects of errors in timing, it is possible for the stacker drum to have a number of suction opening lines, placed side-by-side, so that even after slip or different degrees of slip, the banknotes will still be suction-gripped. However, in this case operation will still not be completely as desired. One shortcoming is produced if a bankpaper getting to the stacker drum overly late does not come into position covering the front suction opening line. Although the suction-gripped banknote will be stacked, there will, however, be a danger of the uncovered suction openings suction-gripping the last banknote stacked beforehand and pushing it against the clearing unit, something which is generally responsible for folding in the case of banknotes in a poor condition. Furthermore, because the suction openings are only partly covered, there may be a great loss in the suction power.
For banknotes getting to the drum before their time, there are the same shortcomings with respect to stacking, as are produced in the case of the firstly noted stacker drum only having a single suction opening line. The leading edges of the banknotes are, in this case, forced violently against the clearing unit, because the complete suction range has an effect, and in most cases the banknotes are folded because of this.